Whether or not you can eat before CT depends on which part of the body is being examined and whether or not an enhanced scan is needed. If it is an abdominal CT examination, fasting is required because of the following two considerations: 1) a large amount of food residue of mixed density in the gastrointestinal tract will interfere with the display of lesions; 2) the gallbladder will contract after a meal, which will affect the judgment of biliary system diseases. However, sometimes in order to better observe the gastric wall, before the examination, the examinee will be allowed to drink 500-1000ml of water, in order to utilize the uniform low density of water to form a good density contrast, and at the same time can fill up the gastric lumen, so that the wrinkled gastric wall will stretch, which is conducive to the observation of the lesion. While CT examination of the intestines is in a different examination purpose, sometimes enema and intracolonic insufflation may also be required, according to the specific requirements of the doctor and the purpose of the examination. When doing enhanced CT examination, from the safety point of view, no matter which part of the enhanced CT, it is best to fasting. Because a small number of people may develop allergy to iodine contrast agent and vomit, it is best to fast for more than 4 hours in order to avoid accidental aspiration of vomit into the airway.